Hi,

a rotary axis is tuned to so many 'steps per degree'. Thus if you have your stepper set for 8 microsteps or 8 x200 =1600 steps/ motor revolution.

With a belt reduction of 4:1 then 4 motor revolutions or 4 x 1600 = 6400 steps per A axis revolution or 6400 / 360 = 17.77 steps per degree. You will have to round to

18 steps per degree but that would result in an error of 1.2%. Not bad.

If you work backwards you may be able to reduce that error a bit. If you assume 18 steps per degree then a full A axis rotation would reuire 360 x 18 =6480 steps.

With the same 1600 steps per motor rev you would require a belt reduction of 6480 / 1600 =4.05. Thus if you have a belt reduction of 4.05:1 instead of 4:1 your steps

per degree would be perfect.

A pulley of 20 an a pulley of 81 teeth would do the trick.

Craig